1. Field of the Invention
The present invention generally relates to light deflectors, light deflection arrays, image forming devices, and projection type image display apparatuses, whereby the direction of outgoing light compared to incident light is changed. For example, the present invention can be used for image forming devices such as electro-photographic type printers or copiers, or projection type image display apparatuses such as projectors or digital theater systems.
2. Description of the Background Art
As a type of light deflector, which moves or transforms a mirror using an electrostatic force, a torsion beam type digital micro mirror device (DMD) has been proposed by L. J. Hornbeck et al. The DMD is a device including a beam and a mirror with a hinge. The beam is twisted at the hinge by electrostatic force. The electrostatic force occurs as a result of different electric potentials applied between electrodes facing each other at a plane surface over an air space. As a result of this, the mirror surface is changed, and therefore light deflection is performed. In addition, the details of the DMD are described in “Proc. SPIE Vol. 1150, pp. 86-102, 1989”.
In addition, as a product using the DMD, a projection type image display apparatus is described in “A MEMS-Based Projection Display Proceedings Of The IEEE, Vol. 86, No. 8, August 1998, page 1687 to page 1704”. Another device, but in which the direction of outgoing light compared to incident light is not changed, is a light valve using a diffraction grating proposed by D. M. Bloom et al. as a typical light modulation apparatus (similar to a light inclination device in a meaning of performing on/off of light). A diffraction grating light valve (GLV) is disclosed in “Optics Letters, Vol. 7, No. 9, pp 688˜pp 690”, Japanese Patent No. 2941952, Japanese Patent No. 3016871, and Japanese Patent No. 3164824. The GLV, as a device including plural elements, has plural long and narrow ribbons of two groups. The ribbons have a light reflection domain in an appearance. The ribbons of the two groups are changed in height by an electrostatic force to produce a potential difference with electrodes, which face the ribbons over an air space. As a result, diffraction of light occurs, a strength of reflection light varies, and light is modulated. In addition, a projection type image display apparatus with the use of GLV is described in Japanese Laid Open Patent Application No. 2002-131838.
The above-discussed background light deflectors include moving or transforming apparatuses like mirrors or ribbons, which have a fixed edge.
FIG. 1 is a view showing a background art light deflector. FIG. 1A is a top view of the light deflector. FIG. 1B is a B-B′ cross-sectional view of FIG. 1. In addition, a light deflector of FIG. 1 is illustrated showing only one light deflector in an array that is arranged in 2 dimensions.
The above described background light deflector is a type in which an incident light beam changes a reflection course in a light reflection area. The light deflector has a substrate 101, plural control members 102, a fulcrum member 103, a plate shape member 104, plural electrodes 105, and an insulation layer 106 (fulcrum member 103 and electrodes 105a to 105d are illustrated with transparency). The plural control members 102 have stoppers in upper parts respectively. The stoppers are provided at plural ends of substrate 101 respectively.
The fulcrum member 103 has a top end, and it is established in the upper side of substrate 101. The plate shape member 104 does not have a fixed edge. In addition, the plate shape member 104 has a light reflection area and a conductive material layer of a member having electroconductivity in at least one part. Plate shape member 104 is deployed to move in the space between insulation layer 106 and fulcrum member 103, but has its movement stopped by the stoppers. The plural electrodes 105 are formed on top of the substrate respectively. In addition, the plural electrodes 105 face a conductive material layer of plate shape member 104. Applying different electrical potentials to the electrodes 105 controls an inclination or slant of the plate shape member 104.
The above-described light deflector has the following advantages:    (a) Control of an inclination corner of a mirror (plate shape member 104) is easy and stable with a dip angle being determined by contact of a fulcrum member and a substrate and a plate shape member,    (b) Reply speed of inclining plate shape member of a film to turn fast at high speed by applying different electrical current potentials to the electrodes can be achieved,    (c) The plate shape member does not have a fixed edge, and thereby there is little long-term deterioration, and the plate shape member can be driven by a low voltage,    (d) There are few shocks by a collision with a stopper as the stopper is small, and a lightweight plate shape member can be formed by a semiconductor process, and there is a little long-term deterioration,    (e) The on/off ratio of reflection light (the S/N ratio in picture machinery, the contrast ratio in picture machinery) can be improved by the constitution of a control member and a plate shape member and its light reflection area,    (f) A miniaturization and an integration are possible at a low cost by employing a semiconductor process,    (g) A light deflection of 2 dimensions of 1 axis and a light deflection of 3 dimensions of 2 axes are possible by disposing plural electrodes.
FIG. 2 and FIG. 3 are examples of a drive method of the above described background light deflector disclosed in prior application Japanese Patent Application No. 2002-282858.
FIG. 2 shows the condition that a plate shape member is inclined by driving as an example with the light deflector of FIG. 1 to be slanted in the position as shown in FIG. 1. FIG. 2A is a cross-sectional view of A-A′ and C-C′ in a STEP 1. FIG. 2B is a cross-sectional view of A-A′ and C-C′ in a STEP 2. In FIG. 2, light deflection movement is performed by changing an electrical current potential applied to electrodes 105a, 105b, 105c, 105d. An occurring electrostatic force (shown by the black arrows) is illustrated by electrical current potential applied as shown in FIG. 2A and FIG. 2B to electrodes 105a to 105d. 
FIG. 3 shows a timing chart of applying the electrical current potential to each electrode of FIG. 2. A drive method of a background light deflector and incline displacement movement of plate shape member 104 (in other words a light deflection operation) are explained in FIG. 2 and FIG. 3. At first, in STEP 1 of FIG. 3, high electrical current potential ‘a’ is applied to electrode 105a, low electrical current potential ‘c’ is applied to electrode 105b, and middle electrical current potential ‘b’ is applied to electrode 105c and electrode 105d. Then, the electrical current potential of the plate shape member 104, which has a conductive material layer facing electrode group 105 and that is floating electrically, becomes equal to middle electrical current potential ‘b’. Therefore, an electrostatic force does not occur at electrodes 105c and 105d of the ON side, but an electrostatic force occurs at electrodes 105a and 105b of the OFF side as shown in FIG. 2A. As a result, plate shape member 104 slants upward toward the OFF side. This movement may be a reset movement to be made at the beginning of a light deflection movement in addition to being at STEP 1 a serial light deflection movement.
Subsequently, in STEP 2 of FIG. 3, high electrical current potential ‘a’ is applied to electrode 105c, low electrical current potential ‘c’ is applied to electrode 105d, and middle electrical current potential ‘b’ is applied to electrode 105a and electrode 105b. Then, the plate shape member 104 floating electrically becomes equal to electrical current potential ‘b’. As a result, an electrostatic force does not occur at electrodes 105a, 105b at the OFF side, but an electrostatic force occurs as shown in FIG. 2B at electrodes 105c and 105d at the ON side. Then, the plate shape member 104 slants upward toward the ON side.
In addition, plate shape member 104 of the above described light deflector may be formed of a single layer in FIG. 1, but it may be preferable to form the plate shape member of plural layers. In addition, in FIG. 2, and the drive of FIG. 3, light deflection movement in an ON direction in 2 dimensions of 1 axis with an OFF direction is described, moving the plate shape member either toward the electrodes 105c, 105d side or electrodes 105a, 105b side. However, the electrodes 105a, 105c side and the electrodes 105b, 105d side the plate shape member 104 can be slanted by changing the voltage applied to electrodes 105a to 105d. In other words, a light deflection of 3 dimensions of 2 axes is possible, if the fulcrum member 103 is arranged as a cone in the center of a light deflector.
FIG. 4 is a view showing a further background art light deflector. In FIG. 4 the plate shape member 104 comes in direct contact with a fulcrum member 103, to constitute a light deflector when applying an electrical current potential to the plate shape member.
FIG. 4A is a top view of a light deflector (but fulcrum member 103 and electrodes 105a to 105d are illustrated with transparence). FIG. 4B is the cross-sectional view of B-B′. In addition, a light deflector described in FIG. 4 is one light deflector in an array that is arranged in 2 dimensions.
FIG. 4 shows a light deflector in which light rays incident on a light reflection area are changed by reflection, by inclining a member having a light reflection area being displaced with an electrostatic force, as in the light deflector of FIG. 1. The light deflector has a substrate 101, plural control members 102, fulcrum member 103, plate shape member 104, and plural electrodes 105. The plural control members 102 have stoppers in the upper parts respectively, and also the plural control members 102 are established in plural ends of substrate 101 respectively. The fulcrum member 103 has a top, and is formed in the upper side of substrate 101. The plate shape member 104 does not have a fixed edge. The plate shape member 104 has a light reflection area and a conductive material layer of at least one part of electroconductivity material. The plate shape member 104 is deployed to be mobile in a space between substrate 101 and fulcrum member 103, and to be stopped by the stoppers. The plural electrodes 105 are provided on top of the substrate respectively, and the plural electrodes 105 face a conductive material layer of the plate shape member 104.
A point of difference from the light deflector of FIG. 1 is in a contact point of a top of fulcrum member 103 contacting at least the back side of plate shape member 104, to have a member having electroconductivity and electrical current potential of plate shape member 104 in contact with fulcrum member 103.
One example of a driving method of the above described background light deflector is explained in FIG. 5 and FIG. 6. The driving method described in FIG. 5 and FIG. 6 is a background driving method. In the driving method an electrical current potential of plate shape member 104 is given by contact with fulcrum member 103.
FIG. 5 shows the condition that a plate shape member is slanted as shown in the light deflector of FIG. 4. FIG. 5A is the cross-sectional view of A-A′ and C-C′ at STEP 1. FIG. 5B is the cross-sectional view of A-A′ and C-C′ at STEP 2.
In FIG. 5, light deflection movement is realized by changing an electrical current potential applied to electrodes 105a to 105d and electrical current potential applied to fulcrum member 103. In addition, an occurring electrostatic force (shown by the black arrows) is illustrated in FIG. 5A and FIG. 5B applied to electrodes 105a to 105d by an applied electrical current potential.
FIG. 6 shows a timing chart of applying an electrical current potential to each electrode of FIG. 5. A drive method of a background light deflector and incline displacement movement of plate shape member 104 (in other words a light deflection operation) are explained in FIG. 5 and FIG. 6.
At first, in STEP 1 of FIG. 6, high electrical current potential X is applied to electrodes 105a and 105b, 0V (the ground electrical current potential) is applied to electrodes 105c and 105d, and the ground electrical current potential is applied to the fulcrum member 103. The fulcrum member 103 includes a laminating with an electroconductivity member or an electroconductivity member, as a structure to which an electrical current potential is applied. The plate shape member 104 coming in contact with the fulcrum member 103 by application of the above-noted electrical current potentials becomes equal with the ground electrical current potential. By it, an electrostatic force does not occur at the electrodes 105c and 105d of the ON side, but occur at the electrodes 105a and 105b of the OFF side, as shown in FIG. 5A. Therefore, plate shape member 104 slants upward toward the OFF side, and is displaced.
In STEP 2 of FIG. 6, high electrical current potential X is applied to the electrodes 105c and 105d, the ground electrical current potential is applied to the electrodes 105c and 105d, and the ground electrical current potential is applied to the fulcrum member 103 continuously. Then, an electrostatic force does not cause the plate shape member 104 to come in contact with the fulcrum member 103 as against electrodes 105a of the OFF side, 105b reaching the ground electrical current potential because it is equal. An electrostatic force occurs as in FIG. 5B at electrodes 105c and 105d of the ON side. Therefore, plate shape member 104 slants upward toward the ON side, and is displaced.
In addition, plate shape member 104 of the above described light deflector can be formed of a single layer in FIG. 4, but may also be formed of plural layers. And also, FIG. 5 and FIG. 6 describe light deflection movement in 2 dimensions of 1 axis to slant toward the electrodes 105c, 105d in the OFF direction and the electrodes 105a, 105b in the ON direction. However, by changing the voltage applied to electrodes 105a to 105d, the plate shape member can be slanted toward the electrodes 105a, 105c in the OFF direction and the electrodes 105b, 105d in the ON direction. In other words, a light deflection of 3 dimensions of 2 axes is possible, if the fulcrum member 103 is arranged as a cone in the center of the light deflector.
In addition, the plate shape member described in FIG. 4, FIG. 5, and FIG. 6 is given electrical current potential via the fulcrum member 103 having electroconductivity, and there is no insulation layer 106 on the fulcrum member 103. Therefore, an electrode must be disposed so that plate shape member 104 does not come in contact with electrodes 105a to 105d on the occasion of slant displacement, as no insulation layer 106 is deployed on the top of electrodes 105a to 105d either.
FIG. 7 is a view of a production process of the light deflector described in FIG. 1. FIG. 7A to 7I are cross-sectional views of B-B′ in FIG. 1.
In the production process of FIG. 7A, the fulcrum member 103 is produced to a desired shape. At first a silicon oxidation layer composing fulcrum member 103 is formed on top of substrate 101 by a plasma CVD method using a phototype process method with the use of a photomask having a cardinality gradation property or a phototype process method to make transform heat after the regist pattern formation. Then the fulcrum member 103 is formed afterwards by a dry etching method. Alternatively, a silicon oxidation layer composing fulcrum member 103 can be formed on silicon substrate 101.
FIG. 7B is a view of a production process of the electrodes 105a, 105b, 105c, and 105d described in FIG. 1. Electrodes 105a to 105d are formed with a film of a nitride titanium (TiN) layer. A TiN film layer is made using Ti targeted DC magnetron sputtering method, and is then patternized as electrodes 105a to 105d of a plural number by a phototype process method and dry etching.
FIG. 7C is a view of a production process of the insulating layer 106 on electrodes 105a to 105d, which is a silicon oxidation layer formed by a plasma CVD method on the electrodes 105a to 105d. 
FIG. 7D is a view of a production process of a first sacrificial layer 401. A silicon layer which is an amorphous substance, is formed by a sputtering method. A planarization is then executed by processing time control by CMP technology. It is important that a film thickness of an amorphous substance silicon layer left on the top top of fulcrum member 103 is controlled. A remaining amorphous substance silicon layer is the first sacrificial layer 401. In addition, as the sacrificial layer, a polyimide layer or photosensitivity organic layer (a resist layer used generally in a semiconductor process) or plural crystallization silicon layers can be used additionally. And also, as a technique of a planarization, a re-flow method and background method by heat-treatment by dry etching can be used.
FIG. 7E is a view of a production process of the plate shape member. The plate shape member has a high light reflection. The plate shape member is made of an aluminum layer accumulated by sputtering to form conductive material layer 104, which is patternized by a phototype process method and dry etching afterwards.
FIG. 7F is a view of a production process of a second sacrificial layer 402. The second sacrificial layer 402 is made of a silicon layer that is an amorphous substance by a sputtering method. In addition, a polyimide layer or photosensitivity organic layer (a resist layer used generally in a semiconductor process) or plural crystallization silicon layers can be used additionally as the sacrificial layer.
FIG. 7G is a view of a production process of the control member 102 having circumferential stoppers that separate individually the light deflector plate shape member 104. By a phototype process method and dry etching, the first sacrificial layer 401 and the second sacrificial layer 402 are compared with plate shape member 104 simultaneously, and are at least somewhat patternized.
FIG. 7H is also a view of a production process of arranging the stoppers around the control member 102. A silicon oxidation layer composing control member 102 having a stopper is formed by a plasma CVD method. By a phototype process method and dry etching, a silicon oxidation layer is patternized afterwards at arbitrary points. In addition, control member 102 having a stopper is not confined to the arrangement shown in FIG. 1. It is preferable that control member 102 is positioned leaving an air space above plate shape member.
FIG. 7I is a view of a production process to be completed for a light deflector. An etching removes the remaining first sacrificial layer 401 and the second sacrificial layer 402 by a wet etching method through an aperture part, to provide a mobile range disposed above plate shape member 104 in an air space. A light deflector is completed therefore. The etching is not limited to wet etching, and sacrificial layer etching can be carried out by dry etching depending on a kind of the sacrificial layer. In addition, as for the sacrificial layer etching, selecting the etching materials is important, as is optimizing materials of plate shape member 104, to make the etching proceed in a substrate planar orientation.
As for the advantages of the above described light deflector, the plate shape member 104 contributing to a light deflection does not have a fixed edge. Therefore, light deflection movement is not accompanied with transformation displacement of a plate shape member (in other words it is exhausted, and it is transformed, and it is twisted, and it is transformed). However, the structure has problems, too. A plate shape member not having a fixed edge moves in an air space limited with a control member. As a result the following problems occur.
FIG. 8 and FIG. 9 are views showing the details of control member 102 at the point D of a light deflector of FIG. 1, and plate shape member 104. FIG. 8 shows the good case that plate shape member 104 does not come in contact with control member 102 having a stopper. FIG. 9 shows a bad case that the plate shape member 104 not having a fixed edge is moved, and completely touches a corner part of control member 102. FIG. 8A and FIG. 9A are top views. FIG. 8B and FIG. 9B are slant views. FIG. 8C and FIG. 9C are cross-sectional views of E-E′.
In FIG. 8 and FIG. 9, 102a is a stopper composed in the upper part of control member 102, and 102b is a support member independently supporting control member 102. In the ideal case described in FIG. 8, friction to prevent movement does not act on the plate shape member 104 as it is displaced around the fulcrum member 103, because plate shape member 104 does not contact support 102b. 
On the other hand, in the case the plate shape member 104 shown in FIG. 9 completely comes in contact with control member 102 in a corner part, a frictional force acts on a movement against displacement of plate shape member 104 as it comes in contact with support member 102b of control member 102 (the white arrow in FIG. 9C). As the size of the control member 102 in a light deflector is comparatively small, when a driving voltage is comparatively high, about several tens of volts, the counter-force of friction does not have a great influence. However, when a driving voltage is comparatively low, about several volts to several tens of volts, there is a possibility of a false operation because of the counter-force of friction, and then a normal slant displacement of plate shape member 104 may not be generated. Paradoxically, an increase in a driving voltage reduces the influence of the frictional force.
The following description is another problem that may occur in plate shape member 104 that does not have a fixed edge with reference to FIG. 10. FIG. 10 is a view of the details of control member 102 shown in the point D of FIG. 1. In the state that a voltage is not applied to electrodes 105a to 105d (initial state), a condition arises in stopper 102a that plate shape member 104 is deployed against the control member 102 upper part.
The plate shape member 104 can move anywhere freely because it is not fixed. When the plate shape member 104 is furthest from electrodes 105a to 105d, the position of the plate shape member 104 becomes as shown in FIG. 10. FIG. 10A is a slant view, and FIG. 10B is a cross-sectional view of E-E′. In FIG. 10, because the plate shape member 104 contacts stopper 102a at a surface, the fixing strength, which is dependent upon surface energy of a layer to contact, begins to act. Then, in an early reset movement shown in FIG. 2A, the voltage to be applied to electrodes 105a to 105d increases to add an electrostatic force to overcome a fixing strength.
As above described, there are drawbacks in the background light deflector making a driving voltage increase by the plate shape member coming in contact with the control member and to overcome the fixing strength.
FIG. 11 is a view of another background light deflector. Problems of this light deflector will be described as follows. FIG. 11A is a top view of a light deflector (but fulcrum member 103 and electrode 105a to 105d are illustrated with transparence). FIG. 11B is a cross-sectional view of B-B′. In addition, a light deflector described in FIG. 11 shows only one light deflector of an array arranged in 2 dimensions. The light deflector described in FIG. 11 shows a constitution approximately similar to the light deflector described in FIG. 1. The point of difference is that the light deflector described in FIG. 11 is a light deflector that can move in only 2 dimensions on 1 axis. Therefore, the fulcrum member 103 is a point having a ridge shape of a length approximately the same as a plate shape member in a light deflection axis direction.
False movement of a light deflection outside a target direction can be restrained by composing fulcrum member 103 to have a ridge shape of a long span. However, there is the following problem by composing fulcrum member 103 to have a ridge shape of a long span.
FIG. 12 is a view of the details of the fulcrum member 103 and the plate shape member 104 of the light deflector described in FIG. 11. FIG. 12A is a top view. FIG. 12B is a cross-sectional view of G-G′. FIG. 12C is a cross-sectional view of H-H′. In FIG. 12, because the plate shape member 104 comes in contact with the fulcrum member 103 along a line, a fixing strength (as shown by the white arrows in FIG. 12C) from surface energy of a layer touching at a contact part arises. Such a fixing strength becomes an obstacle to incline displacement of plate shape member 104. Thereby, an electrostatic force to overcome the fixing strength has to be added. As thus described, a background light deflector has a drawback to make a driving voltage increase by coming in contact with a fulcrum member and to overcome a fixing strength.
Another problem is explained in the light deflector of FIG. 11. FIG. 13 shows the details of fulcrum member 103 and plate shape member 104 and electrodes 105 and insulation layer 106 of the light deflector described in FIG. 11. FIG. 13A is a top view. FIG. 13B is a cross-sectional view on G-G′. FIG. 13C is a cross-sectional view on I-I′.
In FIG. 13, because the plate shape member 104 comes in contact with the insulation layer 106 along a line, the fixing strength (as shown by the white space arrows in FIG. 13C) from surface energy of layers touching in a contact part arises. Such a fixing strength becomes an obstacle to incline displacement of plate shape member 104. Thereby, an electrostatic force to overcome the fixing strength has to be added. As thus described, a background light deflector has a drawback to make a driving voltage increase by coming in contact with a fulcrum member. As thus described, a background light deflector has a further drawback to make a driving voltage increase by coming in contact with the substrate or the insulation layer on a substrate.
The above described background light deflectors has such drawbacks.